Nitrous oxide (N2O) is a greenhouse gas which has 310 times more impact per unit weight than carbon dioxide. It is produced as a by-product in a number of industrial processes including the manufacture of chemicals such as nitric acid.
In many countries limits on nitrous oxide emissions have been set and efforts have been focussed on developing methods to remove nitrous oxide from flue gasses. Many of these efforts have focussed on identifying catalysts suitable for use in the catalytic decomposition of nitrous oxides.
Zeolite-supported iron catalysts, optionally also containing a noble metal such as Pt or Ru, have been described, for example in U.S. Pat. No. 5,171,553, WO 2005/110582 and Journal of Catalysis 243 (2006), 340-349. The major disadvantage of such catalysts is their limited operating window. At temperatures below 400° C., the activity of zeolite-based catalysts become inhibited by water present in the feed. Further, at temperatures above about 600° C. the hydrothermal stability of the zeolite becomes adversely affected.
Other known nitrous oxide decomposition catalysts include those based on base metal oxides such as Co3O4, as described in U.S. Pat. No. 5,705,136. Additional metals, such as nickel, manganese, zinc or magnesium, may be incorporated into the base metal oxide structure as described in Catalysis Communications 4 (2003) 505-509. The addition of alkali-metal promoters to further enhance the catalytic activity of these materials is described in the following documents: Applied Catalysis B: Environmental 78 (008) 242-249; J. Mater. Sci. 46 (2011), 797-805; WO 2009142520, Catalyst Letters, 130 (2009), 637-641; Catalysis Today, 176 (2011), 365-368; Catalysis Today 120, (2007), 145-150; Catalysis Communications, 10 (2008), 132-136; and Catalysis Communications 10 (2009), 1062-1065. Base metal oxides overcome some of the operating window problems associated with zeolite-based catalysts. However, they can have a high bulk density leading to a very high and economically unattractive mass of catalyst required per unit reactor volume.
It would, therefore, be desirable to provide a catalyst suitable for the decomposition of nitrous oxide which can be used at a wide range of temperatures with good stability and life and also has good mechanical properties for a wide range of applications.